Apicidin

TDP-43 proteinopathies, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), are characterized by aberrant cytoplasmic mislocalization and aggregation of TDP-43. Here, we established a live-cell TDP43-BiFC model to visualize TDP-43 oligomerization in real time and screened diverse cellular stressors. Histone deacetylase (HDAC) inhibition emerged as the most potent trigger of TDP-43 oligomerization. In particular, selective inhibition of the shuttling HDAC4/5 with LMK-235 induced an early and robust formation of cytoplasmic TDP-43 oligomers, comparable to or even exceeding the effect of the pan-HDAC inhibitor apicidin. In contrast, nuclear-restricted HDAC1/3 inhibition by MS-275 prolonged TDP-43 retention in the nucleus with minimal cytoplasmic mislocalization or oligomerization, underscoring distinct roles for nuclear versus nucleocytoplasmic HDACs. Inhibition of cytoplasmic HDAC6 (tubastatin A) had no significant effect. Notably, both shuttling and pan-HDAC inhibition increased TDP-43 acetylation and promoted the accumulation of stable, disulfide-linked TDP-43 oligomers. These findings identify lysine acetylation as a key regulator of disulfide bond-dependent TDP-43 oligomerization and suggest that targeting nucleocytoplasmic HDACs could be a novel therapeutic strategy in TDP-43 proteinopathies.

Histone deacetylase (HDAC) density and activity are altered in different brain disorders. Antipsychotic drugs (APs) might modulate HDAC activity in brains of schizophrenia subjects.

HDAC activity assay amenable for enzyme kinetics and HDAC inhibitor (HDACi) screening studies in postmortem human brain samples.

The optimization and characterization work involved several steps. The nucleosolic subcellular fraction and total protein amount needed for an optimal HDAC activity on Boc-Lys(Ac)-AMC substrate were characterized. Signal-to-noise ratio (1.8) and Z-score values (0.82) were indicators of the assay quality. Inhibition studies with non-selective (belinostat, vorinostat, valproic acid) and selective (apicidin, MS275, romidepsin, tacedinaline and EX527) HDACis showed that the optimized assay detected class I HDAC activity. The obtained IC50 values were similar to those previously reported, proving the assay reliability. We used the optimized assay to study the effect of APs on HDAC activity. Inhibition studies with APs in postmortem human brain, together with enzyme kinetic studies in brains of rats chronically treated with APs observed no modulation of class I HDAC activity.

This study describes the optimization of a reliable and cost efficient HDAC activity assay for its use in postmortem human brain samples. The assay does not depend on antibody specificity and it is valid for enzyme kinetic studies and for the screening of new potential class I HDACis.

We optimized and characterized an assay to measure HDAC activity in postmortem human brain samples. We did not observe any modulatory effect of APs on HDAC activity.